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Re: Crystal question

If I recall correctly, it used to be possible to reduce the thickness 
of a crystal to change its frequency, depending on the vibration mode 
of the crystal.  This was done on a lap with the crystal removed from 
its holder -- the modern sealed crystal packages can't be used for 
this, you need a crystal in an old-school crystal holder like the ones 
made by PR.

You have to do this with EXTREME care because this is a one-way change 
in frequency.  I forget which way it goes but if it's the thickness 
mode, it increases the resonant frequency.  There is also a limit to 
how far you can go with this because if you go too far you make the 
crystal too weak and risk cracking it in operation.  It's also possible 
to start small cracks or scratches if you don't lap the crystal too 
carefully and these will also cause the crystal to fail when in-circuit.

If you coat the crystal with resin or something else that keeps it from 
being able to move or vibrate, you'll drastically change the resonant 
frequency or even damp out the resonance entirely, as well as changing 
the capacitance of the terminals and detuning the circuit as a whole.  
It won't make it more temperature unstable, but it'll have really 
unpredictable results in general.  Crystals work best when suspended 
away from any contact with anything but the terminal leads.

On Tuesday, May 6, 2003, at 14:12 US/Central, William Leijenaar wrote:

> Hi AMSATs,
> I like to do some experiments with changing the frequency of normal 
> crystal types.
> I have read in some very old magazines that amateurs did make their 
> needed crystal frequencies themselfs. They take an available crstal 
> and change the frequency of the crystal by changing the shape of it.
> I have tried this also with some crystals I have here, but I was not 
> succesfull.
> Maybe someone knows how to change a crystal frequency without 
> distroying it ????
> And what about the temperature stability ?
> Then some more crystal question:
> --------------------------------
> Can crystals be made (more) shock proof by pour it into resin ?
> Or this will make the crystal more temperature un-stable ??
> 73 de PE1RAH, William

"Many that live deserve death. And some that die deserve
life. Can you give it to them? Then do not be too eager to deal out
death in judgement. Even the very wise cannot see all ends." -- Gandalf

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